This invention relates to rotary screw type pumps, and more particularly to incorporating heat pipe technology into rotary screw type pumps to increase their efficiency.
Screw type pumps are well known, as is shown, for example, by Matsubara et al. U.S. Pat. No. 4,714,418 and Im U.S. Pat. No. 5,667,370. In a conventional screw type pump, the temperature of the pumped gas rises during compression. Compression generally occurs towards the output end of the pump and the temperature of the gas there can increase dramatically. This particularly occurs when the input gas is at a low pressure. The increase in temperature reduces the efficiency of the pump and requires an increase in the operating tolerances within the pump, which increases leakage within the pump.
One current method of decreasing the gas temperature rise is to cool the outer casing of the pump with a water jacket. Another method is to bleed relatively cool gas (e.g., atmospheric air if the pump is pumping air) into the pump or to recirculate some of the output flow, which has undergone cooling, back into the pump. If the input gas pressure is close to or greater than atmospheric pressure, then the gas that is bled into the pump may need to be at a pressure that is greater than atmospheric pressure. While these methods achieve a certain degree of cooling, temperatures in excess of 400xc2x0 F. may still be reached in air vacuum pumps, for example. This large increase in temperature at the output end of the pump causes an axial temperature gradient along the length of the rotors. The large temperature gradient and the differential temperature between the rotors and casing require the pump design to have larger operating clearance than if the parts were more uniform in temperature.
The operating clearance between the rotors and the casing is the controlling factor in the amount of internal leakage within the pump. Internal leakage within the pump is a significant contributing factor to the gas temperature rise at the output end of the pump.
A simple high-flux heat transport device exists that utilizes evaporation, condensation, and capillary action of a working fluid in a sealed container. The high-flux heat transport device is known generally as a heat pipe. The heat pipe was developed for use in a zero gravity space environment. The heat pipe has a very high effective thermal conductivity.
In view of the foregoing, it is an object of this invention to incorporate the heat pipe technology into rotary screw type pumps to increase their efficiency.
It is a more particular object of this invention to decrease the gas temperature rise within the pump.
It is a further object of this invention to decrease the amount of internal leakage within the pump.
These and other objects of the invention are accomplished in accordance with the principles of the invention by providing cavities within the rotors of rotary screw type pumps. The rotors include shaft portions that extend out from the casing that contains the screw portion of the rotors. The shaft portions on the compression side of the pump extend into a chamber and may include fins. The chamber contains a coolant fluid and outside the chamber is a water jacket.
Cavities within the rotors extend from the screw portion of the rotors at the compression side of the chamber to the shaft portion of the rotors. The cavities contain a fluid and may have a porous wick on their surfaces. During operating of the pump, as the gas temperature increases due to compression, the fluid within the screw portion of the rotors evaporates in the portion of the cavities within the screw portion of the rotors. The evaporated fluid then condenses in the portion of the cavities that are in the chamber. The wick facilitates the movement of the condensed fluid back to the portion of the cavities within the screw portion of the rotors. The wick may not be required in all embodiments for satisfactory operation of the apparatus.
This process removes the heat generated during gas compression within the casing and transfers the heat to the shaft portion of the rotors. The heat is transferred from the shaft portion of the rotors to the coolant and then the water jacket for removal.
Further features of the invention, its nature and various advantages will be more apparent from the accompanying drawings and the following detailed description of the preferred embodiments.